Lab tests for testosterone levels are not that reliable

DEAR DOCTOR K: I've been having symptoms that may be caused by low testosterone. I figured it would be easy to test my testosterone levels, but my doctor says it's complicated. Why?

DEAR READER: Testosterone is one of the main male hormones. Blood levels of this hormone start to sag in early adulthood, and then creep lower. In some men, the levels become low enough to cause symptoms. The classic symptoms of low testosterone ("low T") are low sex drive, erectile dysfunction, poor muscle tone, poor concentration and memory, and low energy. However, these same symptoms can result from other illnesses, including depression and heart disease.

What makes testing for low T tricky is that levels of the hormone change during the day, and also that the hormone exists in two different forms in the blood.

Testosterone levels are highest in the morning. Blood for testosterone lab tests should be drawn between 7 a.m. and 10 a.m. Based on this blood test, your doctor must determine if your total testosterone level is low. Unfortunately, different laboratories measure total testosterone using different methods. That means there is no standard definition of "low": Every laboratory has its own definition.

Even more confusing, the total testosterone value isn't what's really important. Here's why: Most of the testosterone in your blood is attached to a protein. The protein holds it tight and releases only some of it.

Testosterone can't have any effect on your body unless it is floating freely in the blood. A man can have normal or even high levels of total testosterone, but low levels of free testosterone. (I've put an illustration of what makes up total testosterone on my website, http://AskDoctorK.com.)

It's the free hormone that has the effects that a man with low T wants: sex drive, erection, good muscle tone, improved concentration and memory, and more energy. So it would seem logical, then, just to test free testosterone. Unfortunately, lab tests for free testosterone are even less reliable than tests for total testosterone.

Why not simply treat low testosterone if your symptoms and tests suggest low T? Because treatment -- testosterone replacement -- can have side effects of its own. These include increased risk of blood clotting. There's also concern that testosterone supplementation could trigger prostate cancer, or speed up tumor growth in men who already have prostate cancer. On the other hand, there also is evidence that men who normally have low testosterone levels may have a greater risk of developing prostate cancer.

There also is a concern that testosterone therapy might increase the risk of heart disease. In one relatively small study of old and frail men with multiple chronic diseases, there was a suggestion of an increased heart risk.

So, your doctor said it was complicated -- and you were probably hoping I could make it uncomplicated. Unfortunately, I'm going to disappoint you on this question. The research is incomplete, and the blood tests are wanting.